Human lips are prone to sun damage when exposed to UVA and/or UVB radiation. Efficacious protection from UVA and UVB radiation requires the use of significant amounts of sunscreen and often a mixture of organic sunscreens to achieve efficacious protection from both UVA and UVB radiation. UVB, which is radiation in the wavelength range of 290 nm-320 nm, has been characterized traditionally as the sunburn radiation as it is the radiation that typically produces redness of the skin. In addition to producing redness, it can decrease enzymatic and non-enzymatic antioxiants in the skin and impair the natural protective mechanisms in the skin contributing to DNA damage and potential skin cancer. The dangers of UVA radiation, which is radiation in the wavelength range of 320 nm to 400 nm, have only recently been recognized. Chronic exposure to UVA radiation can cause damage to gene P53 DNA, possibly leading to cancer. Additionally, the longer UVA wavelengths allow for relatively deep penetration into the skin tissues causing damage to the elastic fibers and collagen which give skin its shape, thus causing wrinkling and eventually premature skin aging. Thus, protecting the skin including the skin of the lips from UBA and UVB is important to maintenance of skin health and appearance.
Unfortunately, sunscreens, particularly organic sunscreens, have a bad taste. Some sunscreens including avobenzone which is particularly useful for UVA protection have a very bad taste. This bad taste is not an issue for lotions that are applied to the body to protect body surfaces from the sun damage, but become a significant problem when sunscreens are incorporated into lip treatment compositions. Unfortunately, there are no other available sunscreens which afford UVA protection as effectively as avobenzone.
Prior to the present invention, forming a lip balm or treatment with levels of sunscreen that that would have an efficacy of SPF 30 or greater (i.e., significant UVB protection) has yielded compositions that have a very unpleasant taste. The taste is sufficiently unpleasant to discourage use and/or result in limited compliance. Commercial lip products with SPF 30 or greater protection claims are widely recognized to be bad tasting. The addition of avobenzone to such compositions to provide UVA protection exacerbates the problem significantly.
Conventionally, sweeteners and/or flavorants have been used to cover or mask unpleasant tastes. In this approach, the sweetener and/or flavorant competes with the undesirable taste. While this may be successful in some applications, it is not satisfactory for masking the taste of the very strong and/or bitter flavors of organic sunscreens. Additionally, the flavor and/or sweetener may lack the persistence of taste over the entire time frame that the sunscreen remains on the lips, resulting in the evolution of a distasteful sensation after a period of time.
Coatings and forms of encapsulation are other approaches for taste-masking. However, coatings and/or encapsulation may alter the reactivity or release of the active agent. Further, coating or encapsulation of a bad tasting material in a lip product is typically an even more difficult problem than taste-masking of an ingested material, as unlike ingested materials, the product is intended to stay on the lips for a period of several hours. The integrity of the coating upon the lips must be maintained for a period of several minutes to several hours. The integrity of the coating upon exposure air, moisture and or light must be maintained over a period of many times longer than the period of time needed to swallow an ingestible composition.
In addition to the need to maintain taste-masking over a long period of use, in the case of the sunscreen in a lip balm, the taste-masking mechanism should not impair the sunscreen's function of protecting the lip tissue from UVA and/or UVB radiation.